Variable fuel neutronic reactor



Feb. 12, 1963 w. A. FREDERICK I VARIABLE FUEL NEUTRONIC REACTOR 5Sheets-Sheet 1 Filed Sept. 2, 1958 INVENTOR William A.Frederi0kwp'ruzsses AT NEY Feb. 12, 1963 W. A. FREDERICK VARIABLE FUEL NEUTRONICREACTOR Filed Sept. 2; 1958 5 Sheets-Sheet 5 8 5 82 m 8 3 42 l f m 2 s 6.N 4 M o M 2 m 0 I a a .4. m 4 521m I H 3 .m 9.: 5.1 25 T|F a z 0 w s 4m 3 3 6 8 B g 3 CM. WW II :6 2 I .zzsunow 2 W 6 0 a h C i new m F '2 2 n0 9 m L A 5 5 .T .l m 1 Q. 1 4 M F. Jm; 0 m. 2% m n m 2:32am 8 w H m 2 m0 M r 8 -E B mIt-i 87 a 4 4 1 2 055.3: 25 fi l 3 4 B h a o 3 .l n m r we4 I O.- C v 3 8 .M m u i a H 0 3. B a vs ad w w 6 w c w o W Lu II 9 l 4.k M 8 7 6 3 m w r .8 x .M 2 4 0 0 x 8 w -3Eonu u J 9 5 k H. I. m n Y I0 R T x n 0 m P L" am. 4 O 4 r a 7 0 b D 6 m r 0 0 4 6 7 I- 2 c 335:; Mw. 4 w v E r I M C D a I H 9 9 w O S MH r r 2 2 6 I 8 2 a .W M 2 4 I. I3| 3 Sh 2 M m;

Feb. 12, 1963 w. A. FREDERICK 3,077,445

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Feb. 12, 1963 w. A. FREDERICK VARIABLE FUEL NEUTRONIC REACTOR FiledSept. 2, 1958 5 Sheets-Sheet 5 0 160,260 300 460 soo e00 100 Grams of'Thoriurn/Kiloqrarn of 0 0 Vessel Manifold Vessel Manifold I346 CoreAverage Generator Outlet v2 5}: Fraction of Full Power 3,077,445VARIABLE FUELNEUTRONIC REACTGR William A. Frederick, Monroeville, Pa.,assignor to Westinghouse Electric CorporatiomEast Pittsburgh, Pa.,;a

corporationxct Pennsylvania Filed Sept. 2, 1958, Ser. No. 758,341

- 4 Claims. (C 2e4 19s.2

The present invention relates to a neutronic reactor and moreparticularly to apparatus associated therewith for use in starting typereactor. 1

Incertain types of neutronic reactors, an example of i whichis'described hereinafter-in'greater detail, the reactor and the primarycirculating systems associated.

therewith are arranged for supplying nuclear fuel or fissile material tothe reactor in varying masses or concentra or in a form of largerdiscrete particles either of which may be supported by a gas or othervehicular fluid. In still otherneut-ronic reactor systems the fissilematerial canbe supplied to the reactor vessel in the formsofametallo-organic compound of the fissile material which is a liquid atreactor operating temperatures, a solution of a soluble fissile materialsuch as uranyl-sul-fate, or tree suspension or slurry of desirably ultrafine particles of the fissile material or their oxides in a suitablevehicle such as that described hereinafter. Although the inventiondisclosed herein is adapted for use in operating many of theaforementioned variable concentratiom type reactors, the invention willbe described in greater detail in connection with a quasi-homogeneous,slurrytype reactor.

It has been found in certain neutronic reactors, wherein theconcentration of the fuel can be varied readily, that there are twoconcentrations of the fuel whereat the neutronic reactor can reachcriticality at a given operating temperature. These concentrations aredesignated asthe high and low critical concentrations respectively.

However, in the range of fuel concentrations between these criticalconcentrations, the reactor would become supercritical if thetemperature remained more or less constant and if no means were employedto control the reactor. It is desirable, however, to operate theneutronlc reactor at'the high critical concentrationfor the reason thatwith the added fissile material included within the reactor vessel agreater neutronic economy is ob-' tained; and hence a greater conversionratio of the fertile. isotope, usually included in the fissile material,to one of the fissionable isotopes is likewise secured. It has likewisebeen found that when operating an eificient neutronic reactor at thehigh criticalconcentration that conversion ratios of unity or greatercan be obtained, that is to say, that at least as much fissionableisotope is transmuted from the fertile material as is consumed in thechain reaction sustained in the initial supply of fissionable isotope.The basic mechanisms whereby the fertile isotopes are converted into thecorresponding fissionable isotopes in a neutronic reactor aredescribedhereinafter in greater detail.

As. pointed out previously, the reactor temperatures correspondingto-the aforementioned high and low critical concentrations aresubstantially the same. However, the

up and shutting down a variable fuel average temperature of the reactorrises to a high peak between these two points .as the concentration israised from the low critical point to the 'hig'h critical point 'ifaIIptherjfactors'remairi the 'same, This: condition results :intheaforementioned supercritical condition where intheietlective constantjofcriticality m would become slightly greater than unityatconcentrations between these critical pointsQif the temperature wereto remain constant. The' temperature upswing in certain cases, however,is sufiiciently high, ifuncontrollemto' sociated prirnary equipment. H vi v In spiteiof he foregoing remarks, it has been found that the safestmethod of adding. fissile material to the reactor is to fill the primaryreactor system initially with either a dilute mixture. of fissilematerial and a suitable vehicle or with the vehiclefalone. The dilutemixture, if employed, is maintained'at a concentration which is exceedthe design limitationsof the reactor andv the assufiiciently low topreclude criticality under any conditions. Theconcentra tionof fissilematerial then is gradually increased through thelowcritical'concentration to the high critical concentrationor operatingconcentration.

As the concentration is increased between the low and high criticalconcentrations, suitable means are employed to control the reactor inthe, areaof s'upercriticality between theseconcentrations. Desirably,the reactoris operated for a' time at the low critical concentration in'order to produce sulficient internal Xe to shut down the reactor whilethe concentration is being increased from the. low tothe high criticalconcentration. 'This method of operating the reactor is described fullyand claimed in a copending applicationof William A. Frederick, entitledMethod of Operating A Nuclear Reactor, filed December 20,1957, .S.N.704,098, and assigned to the present assignee. Alternatively, anexternal reactor poi-- son, for example a boronic compound, can be addedto the primary system in accordance with known methods; or on the otherhand the primary reactor system can be designed to withstand the highertemperature necessary to shut down the reactor due to the negativecoefiicient of reactivity exhibited by thermal and epithermal reactorsand described hereinafter.

It may be sugegsted that the reactor system be filled initially withfissile material at a concentration above the high criticalconcentration, which is then gradually reduced to the operatingconcentration. This method is not feasible due to the possibility of aportion of fissile materialsettling out of the vehicle afteraddition tothe reactor, particularly before the circulating pumps can be started,and to the attendant great danger of unpredictable criticality in thefissile material when thus diluted. Moreover, the fissile material wouldhave to be main tained at anincreasingly high temperature as theconcentration is reduced in order to preclude premature criticality.For. practical purposes, then, the reactor system would have to beraised to operating temperature by means of an external source of. heat.before beginning to decrease the concentration of fissile material.

It may be suggested also that the primary reactor system be filledinitially with fissile material at the operating or high criticalconcentration. This method likewise is inappropriate due tounpredictable reactivity of the fissile material while being added inthis concentration. Both thereactor system, and :fissile material. wouldhave to be preheated in some fashion to a temperature in excess ofoperating temperature to prevent premature 'criticality and thermalstresses in the reactor'. system. Moreover,- when employing certaintypes of vehicles for the fissile materiaL-these vehiclesmustbemaintained under considerable pressures to prevent boiling at theoperating reactor: temperatures. However, the required pressurizPatented Feb. 12, 1963 ing is impractical until the reactor system,including usually a reactor vessel and a number of circulating orcooling loops, is completely filled. Furthermore, the primarycirculating pumps cannot be started until the reactor system iscompletely filled, if the fissile material is in liquid form, because ofvapor binding. Consequently, a portion of the fissile material maysettle out of the vehicle, whereupon the concentration of the remainingfissile material may fall into the aforementioned supercritical areabetween the low and high critical concentrations.

Specifically, the invention relates to apparatus for use in starting upand shutting down a neutronic reactor so that the reactor can beinitially filled either with a very dilute mixture of fissile materialin a suitable vehicle or with the vehicle alone. Subsequently, theconcentration of the fissile material is gradually increased by meansprovided in accordance with the'invention until the desired operatingconcentration is attained. In shutting down the reactor the reverseprocedure is followed. The aforementioned apparatus is arranged so thatthe rate of increase or decrease in fissile concentration within theprimary reactor system can be readily changed or otherwise controlled inorder to avoid large inputs of reactivity in the primary reactor system.Although the invention is described hereinafter in conjunction with aslurry type homogeneous reactor having high and low critical fuelconcentrations, it will be obvious as this description proceeds that theinvention is not limited thereto.

In view of the foregoing it is an object of the invention to provide anovel and efiicient neutronic reactor system particularly of the type inwhich the fuel concentration thereof can be readily varied.

Another object of the invention is to provide novel apparatus adaptedfor use with a neutronic reactor for the purpose of facilitating fillingand draining the primary system thereof.

Still another object of the invention is to provide apparatus of thecharacter described for varying the concentration of a homogenous orquasi-homogeneous type reactor in a carefully controllable manner.

A further object is the provision of apapratus of the characterdescribed which is adapted for coupling to the primary circulatingsystem of a reactor and which is operable without the use of additionalpumping means.

These and other objects, features and advantages of the invention willbe made apparent during the forthcoming description of an illustrativeembodiment of the invention with the description being taken inconjunction with the accompanying drawings wherein:

FIG. 1 is a schematic and elevational view, partially sectioned, of anexemplary homogeneous-type reactor vessel shown in conjunction withprimary coolant loop circuitry;

FIGS. 2A, 2B, 2C constitute a schematic fluid circuit diagram of ahomogeneous reactor system such as that illustrated more generally inFIG. 1 and arranged for use with certain auxiliary equipment;

FIG. 3 is a graph showing a series of temperature curves of theeffective neutronic multiplication constant plotted against slurryconcentration; and

FIG. 4 is a graphical representation of slurry and steam temperatures ofthe reactor system described herein, as

functions of reactor power output.

Generally speaking, in a homogeneous-type reactor system, the nuclearfuel is contained within the system as a liquid or suspension, which insome cases may be a liquid compound of at least one of the fissileisotopes noted below. a suspension in a suitable vehicle of apulverulent form of one or more of these fissionable and fertileisotopes, or a combination thereof, or a solution of one or morecompounds thereof in a suitable solvent such as water. In those systemswherein the fuel is employed as a conventional suspension or slurry orin some other fluidized form wherein the fuel is present in discrete,movable par- In other cases, the liquid fuel comprises.

ticles, the reactor system is sometimes designated as quasihomogeneous.As explained more thoroughly hereinafter, the fluidized fuel iscirculated through a reactor vessel by one or more primary circulatingloops provided with suitable pumping means. The fluid fuel including thevehicle or solvent, which usually serves both as coolant and moderator,thus circulates through both the vessel and the circulating loops incontradistinction to a heterogeneous type reactor system. In the laterclass of reactors the fuel, moderator, and the coolant orcoolantmoderator usually are physically separated and at least the fuelis mounted fixedly and entirely within the reactor vessel.

The homogeneous reactor vessel is fabricated of such size and shape thata quantity of the circulating fluid fuel contained therein is equivalentto the critical mass of the chain-reacting isotope included in the fueland consequently a self-sustaining chain reaction can be established inthe vessel. In the case of a quasi-homogeneous reactor, theconcentration of the fissionable or chain-reacting isotope in the slurryor suspension can be adjusted within rather wide limits such that theaforesaid size and shape of the vessel can be varied accordingly asdesired. As pointed out hereinafter, the remaining components of thesystem are insufficient in size and are suitably spaced or shielded suchthat a critical mass cannot be accumulated elsewhere in the reactorsystem. The heat developed within the circulating fuel as a result ofthe nuclear chain reaction is removed from the fuel as it circulatesthrough the primary loops by suitable heat exchanging means coupledwithin each of these loops.

The vehicle or solvent employed with the circulating fuel, which may beordinary water (H O), heavy water (D 0) or an organic material havingthe desired characteristics of temperature and radiation stability,serves as a moderator for the chain reaction in addition to serving as aheat transfer medium as noted heretofore. As is well known, a moderatormaterial usually is employed adjacent the nuclear fuel to slow the fastneutrons produced by each fission to thermal velocity, whereat theneutrons are most efficient for inducing fission in atoms comprising thefissionable isotopes. More specifically, the moderator material slowsneutrons having energies in the neighborhood of ten million electronvolts to energies which are equivalent to thermally excited hydrogenatoms or about 0.1 electron volt. As a result, the mod erator materialappropriately is selected from a material having the characteristics oflow neutronic capture crosssection and a high neutronic scatteringcross-section. Suitable materials for these purposes include carbon andthe vehicles or solvents noted heretofore, i.e., light and heavy water,and hydrocarbon organic materials which, of course, contain carbon andhydrogen.

1 The homogeneous reactor system, presently to be described, iscontrolled inherently by the negative tempera ture coefficient ofreactivity associated with the circulating nuclear fuel. This phenomenomis comparatively well known and is based upon the fact that an increasein temperature of the fuel contained within the reactor vessel decreasesthe density of both the fuel and the vehicu lar moderator and likewiseits moderating characteristics. By the same token, this decrease indensity increases the number of neutrons which are lost from theperiphery of the chain-reacting mass, and the resulting loss in neutroneconomy decreases the reactivity of the reactor system. Additionalcontrol is accomplished, as required, by diluting the circulating fuelwith additional vehicle or solvent, by adding a neutron absorbing poisonsuch as cadmium, boron, or xenon, or by draining the contents of thereactor vessel into a series of storage tanks presently to be described.The latter arrangement also serves to terminate the chain reactioncompletely in an emergency or to shut down the reactor for maintenanceand the like.

The fissional products which are formed during operation of the reactordesirably are extracted continually from the system by means of chemicalprocessing in the case of solids, or in the case of gases, by means ofan spectively, and both assigned to the present assignee.

These fissional products cannot be permitted to accumulate within thereactor system during normal operation thereof inasmuch as some of thedaughter isotopes, particularly xenon 135, quickly terminate or poisonthe chain reaction although present in relatively small concentrations.As pointed out hereinafter in greater detail, use can be made of thisfact in controlling and operating a variable fuel concentration typereactor. In any event, the accumulation of these isotopes which resulteither directly, or indirectly through radioactive decay, from thefissional process would tend to increase radioactivity associated withthe reactor plant as compared to the conditions obtaining were thefissional products continuously removed. As a result, the normalbiological shielding requirements for the reactor vessel, the fuelcirculating loops, and associated equipment would be increased.Moreover, many of the longer-lived, fission-produced isotopes arevaluable per se for those research, industrial, and medicinalapplications, which require high levels of the various radioactiveemanations.

The circulating nuclear fuel in a simple burner type homogeneousreactor, contains a high percentage of one or more of the knownfissionable isotopes U U Po amounting of course, to a quantitysufficient to sustain a chain reaction. Although a simple burner type ofreactor is relatively more efficient as to size and neutron economy, itsinitial fuel cost is very high. Moreover, substantially no additionalfuel is produced during operation of this type of nuclear reactor. Onthe other hand, in regenerative or breeder types of homogeneousreactors, an additional quantity of a fertile isotope such as Th or U isadmixed uniformly with the circulating fuel material. Thelatter-mentioned fertile isotope can be supplied in the form of naturalor source grade uranium which is primarily the U isotope containingapproximately 0.7% of U In a heterogenous type reactor, the samecombinations of fissionable and fertile isotopes can be employed, withthe exception that both groups of the fissile isotopes are fixedlymounted within the reactor core and that the fertile isotope, commonlyreferred to as blanket material, usually surrounds the fissionablematerial. However, in a uniform, low enrichment heterogeneous reactor,several designs of which are either extent or under consideration, thesocalled blanket or fertile material, of course, is mixed uniformly withthe fissionable isotope. In the latter class of reactors, U usually isemployed which has been enriched to a greater than natural percentage ofU In an ei-ficient reactor of the previously-mentioned regenerativetypes, it is possible to generate from the one or more fertile isotopesat least as much fissionable isotopes as is consumed in the chainreaction. If the conversional ratio is greater than unity, the reactoris classified in the breeder category.

During the progress of the chain reaction, each fissioned atom emits anaverage of two to three neutrons, some of which are classified as fastneutrons and must be slowed to thermal energies as noted previously.Approximately one of these neutrons is utilized in prop-agating thechain reaction. Another one of the neutrons is employed to initiate oneof the series of nuclear reactions described below, whereby an atom ofthe fertile or blanket material is transmuted into an atom offissionable isotope, and the amount thereof may be equivalent, forexample, to the amount of fissionable material consumed in the chainreaction. If such is the case, only the fertile material need be addedto the reactor system during its operation. The remainder of thefission-produced neutrons are absorbed in structural and moderatormaterials, in non-fissioning capture of atoms of fissile material, andin peripherales'cape from the chain-reacting mass.

'Upon capturing one of the aforesaid fissional neutrons the fertile-material U if employed, is converted into angisotope-of the transuranicelement plutonium Pu in accordance with the following nuclear equations:1 I

23 min.

23 min.

The resultant fissionable isotope U having a half-life of 163,000 years,likewise is relatively stable.

Referring now mor specifically to FIG. 1 of the draw ings, an exemplaryvariable fuel concentration type of reactor system is disclosed, whichis adapted for operation in accordance with the invention. In thisexample, the reaction system is a quasi-homogeneous, or slurrytypesystem, and comprises a reactor vessel 20 having a spheroidalconfiguration and provided at'diametrically opposite areas thereof withinlet and outlet manifolds 22 and 24, respectively. The reactor vessel24 is of sufficient size to contain, as aforesaid, a critical mass ofthe circulating nuclear fuel flowing through the vessel and the primaryloops of the reactor system. In this application, wherein a circulatingslurry containing suspended, uniformly, admixed, pulverulent oxides ofthorium (ThO- and highly enriched uranium U0 is employed, with a vehicleincluding deuterium oxide or heavy water (D 0), the inside diameter ofthe innermost reactor vessel thermal shield 41) is of the order of 13feet. The aforementioned slurry, which is described subsequently ingreater detail, thus includes a fissionable material in the form ofuranium 235 and a fertile material, thorium 232. Additionally, a smallproportion of the fertile material, uranium 238, is included unavoidablywith the U isotope.

In this example of the homogeneous reactor system a total of fourcirculating loops, with only one loop 25 being shown in FIGS. 1 and 2,are connected to the intake and outlet manifolds 22 and 24 by means ofinlet and outlet conduits 26 and 23, respectively. The outlet conduit 28is connected to a gas separator 39 which in turn is coupled in serieswith a steam generating heat exchanger 32 coupled through a conduit 35to the suctional side 34 of a primary slurry pump 36. The gas separator36 is designed in a conventional manner and is arranged to removefissional and radiolytic gases from the system, which gases areconducted out of the separator by means of a conduit 31. The steamgenerator 32 which is provided, inter alia, with a feed Water inlet 33and a steam outlet conduit 37 is constructed similarly to that describedin a copending application of William A. Webb et al., entitled RemoteEquipment Maintenance, Serial No. 659,002, filed May 15, 1957, nowabandoned, and assigned to the present assignee. The discharge side ofthe'pump 36 is coupled to the inlet conduit 26 and manifold 22 of thereactor vessel.

In this example, the reactor vessel 26) is formed from a plurality ofspheroidal sections 3% which are welded together as shown to form thecompleted vessel. In order to minimize neutron-induced thermal stresseswithin the walls of the vessels 29, which are of the order of six andone-half inches in thickness, a plurality of thermal shields, indicatedgenerally by the reference character 40, are disposed adjacent the innersurface of the reactor vessel walls. The thermal shields 40 conformgenerally to the inner configuration of the vessel walls and are spacedtherefrom and from one another in order to provide, in this example,flow channels therebetween for the passage of a peripheral portion ofthe circulating nuclear fuel. Inasmuch as the thermal shields 40 aresubjected to little or no pressure difierentials, they are maderelatively thin with respect to the vessel walls 20. A plurality ofbattles 42 are disposed adjacent the lower or intake manifold 22 and aresuitably shaped for distributing the incoming slurry as indicated byflow arrows 44 throughout the interior areas of the vessel 20 and fordiverting a peripheral portion of this flow through the passages formedbetween the thermal shields 40 and adjacent the inner wall of the vessel20 A neutron reflecting member (not shown) can be disposed adjacent thethermal shields to reflect peripheral neutrons back into the centralregion of the vessel 20 in order to improve the neutron economy of thechain reaction.

The disposition of the thermal shields 40 in this man ner substantiallyprevents impingement of fission-neutrons upon the adjacent vessel walls.Accordingly, the heating effect of the impinging neutrons is developedalmost entirely within the thermal shields 40 which are not subject topressure stresses as are the Walls of the pressurized vessel 20.Moreover, the heat developed within the thermal shields 40 is readilyremoved by the peripheral portion of the circulating fuel flowingthrough the channels therebetween. Alternatively, the thermal shields 40can be replaced by the shield arrangement disclosed and claimed in acopending application of W. P. Haass, entitled Reactional Vessel, SerialNo. 652,627, filed April 12, 1957, and assigned to the present assignee.

The pressurized reactor vessel 20 is mounted upon an annular supportingcollar indicated generally by the reference character 26 and mountedupon a biological shielding wall portion or support 48. This mountingarrangement for the reactor vessel 20 and the physical distribution ofthe primary circulating loops and other equipment associated therewithare described in greater detail in a copending application of W. A. Webbet al., entitled Reactor Plant, Serial No. 659,004, and assigned to theassignee of the present invention.

In order to drain the contents of the reactor vessel, a drain outlet 50disposed in the lower or intake manitold 22 is coupled to a series ofslurry drain tanks 52, through a conduit 54. When it is .desired to fillthe reactor system, the slurry contained in the drain tanks 52 isreturned through another conduit 56 which is coupled to one or more ofthe circulating loop conduits 35. To aid in filling the reactor vesseland associated loops, an auxiliary slurry pump is coupled into theconduit 56. The physical disposition of the drain tanks 52 relative tothe nuclear power plant arrangement is described in greater detail inthe last mentioned copending applica tion. For the present, it may bepointed out that the drain tanks 52 are provided in suilicient number tocontain at least all of the circulating nuclear fuel slurry of thesystem but are of such size that none of the tanks can contain acritical mass of slurry. Suitable neutronabsorbing material (not shown)is disposed between adjacent tanks in order to prevent the developmentof a chain reaction within the collective group of tanks when they arefilled with tr e circulating fuel.

In one exemplary arrangement, the fluid fuel contained within each ofthe drain tanks 52. is stirred constantly by individual agitators andstirrers 59 mounted adjacent the top of each of the tanks 52. The tanks52 and the agitators desirably are hermetically sealed to preventleakage of biologically hazardous fluid and desirably are provided inthe form at that disclosed and claimed in a copending application of Meiand Widmer, entitled seared Agitator, Serial No. 672,661, filed Zui 18,1957,

means of a conduit 66.

8 now'US. Patent No. 2,907,552, and assigned to the present assignee.

The upper or outlet header 24 is fitted with an additional port 60 towhich a surge tank 62 is coupled by in one form of homogeneous reactorsystem, the surge tank s2 comprises a relatively large volume which,however, is insufficient to contain a critical mass of the circulatingfuel. When in operation, a vapor space 63 is formed in the surge tank,which conveniently contains a vapor of the vehicle employed insuspending the aforementioned fissionable and fertile oxides. As aresult, during a positive system. transient within the homogeneousreactor system, a surge of liquid into the tank d2 compresses the vaporconfined within the surge tank space as, thereby relieving at leastpartially the increased pressures developed within the system.

A pressurizing vessel 64, which is coupled to the surge tank 62 by aconduit 6? connecting the vapor spaces thereof, is furnished with anumber of heating elements, indicated generally by the referencecharacters 70 and arranged for heating a portion of liquid, desirablythe same as the aforementioned liquid vehicle of the system. Thus, thereactor system is maintainedat the desired operating pressure, byvaporization of the aforesaid vehicle portion. As a corollary functionthe pressurizing vessel 64 operates to maintain the aforementioned vaporspace or surge volumes 68 within the surge tank 62. The pressurizingvessel 64 is provided with an inlet conduit 72 whereby the vessel 64 isinitially charged with the aforesaid vehicle portion and make-up vehicleis added to the pressurizing vessel as required.

Alternatively, the pressurizing vessel 64 and the surge tank 62 can bereplaced by the pressure regulating systern claimed and disclosed in acopending application of Jules Wainrib, entitled Pressure ControllingSystem, Serial No. 677,942, filed August 13, 1957, now US. Patent3,060,110, and assigned to the present assignee.

Referring now more particularly to FIG. 2 of the drawings, the variousauxiliary equipment associated with the aforedescribed homogeneousreactor system, is illustrated schematically therein. In the arrangementof the homogeneous reactor system, illustrated in FIG. 2, the primaryslurry pump 36 is furnished with a capacity of approximately 8,000gallons per minute which in conjunction with three other primary slurrypumps (not shown) disposed in a like number of similar circulating loopsystems indicated generally by arrows 25, produces a total rate of flowof approximately 32,000 gallons per minute. inasmuch as the reactorvessel 20 and the circulating loops together enclose a total volume ofapproximately 19,000 gallons, the circulating fuel is recycled throughthe system in about one-half minute.

In this application of the invention, the circulating slurry comprises avehicle of deuterium oxide (B 0) in which is suspended about 300 gramsof thorium oxide ('ihO per kilogram of D 0 and approximately ten gramsof uranium oxide (U0 per kilogram of D 0. The uranium in this example isfully enriched and contains upwards of of U isotope. Added with theuranium oxide is a very small proportion of a palladium catalystemployed to promote internal recombination of the major proportion ofthe radiolytic vehicular gases, deuterium and oxygen. The uncombined orremaining radiolytic gases are employed to sweep fissional product gasesout of the system, as explained hereinafter. The quantity of palladiumcatalyst, which is added in the form of the oxide (PdO) is of the orderof 0.001 gram per liter of slurry and can be replacethif desired, byother suitable catalysts, for example, a platinum compound.

Accordingly, the system circulates a mixed oxide slurry with a totaloxide concentration in excess of 300 grams per kilogram of D 0 whichcorresponds to a solids content of about 3% by volume. The reactorvessel 20 and the circulating loops 25 are maintained under a pres- 11the conduit 1% and in the conduit 54. In this manner the reactor vessel2% and each of the four circulating loops 25 are coupled through thedrain header 96, a normally opened valve 198 in the drain header 96, andthe drain tank inlet conduits SC to the thirteen slurry repository tanks52'C.

By suitably opening one or all of the valves 1% or. 162 in the drainheader conduit 96 the slurry accumulator tank SZ'A in an emergency canbe utilized either with the group of six concentrated slurry tanks orwith the group of thirteen slurry repository tanks 52'C.

Thus, it will be seen that the drain header 96 mainly serves to connecta total of nine points of drainage i.e., one at the reactor vessel 21)itself and two at each of the primary loops '74, from the primaryreactor system to the drain tanks 52. Among the auxiliary functions ofthe drain header 96 are transfer of deuterium oxide steam from asuitable evaporator (not shown) to the drain tanks 52' for heating andpressurizing the drain tanks 52 to prevent thermal shock upon contact byhot slurry drained from the primary reactor system, return of conrdenseddeuterium oxide from a plurality of condensers 11-; and 115 presently tobe described to the drain tanks 52 and transfer of material from onedrain tank to another in the manner presently described.

Each of the twenty drain tanks 52' also is coupled to the liquid headeror conduit 11% by means of individual valved conduits 112. If desired, asmall portion of slurry can be \drawn periodically from the drain tanks52' and conducted by means of the liquid header conduit 110 and aconduit 116 to a chemical processing plant 118. At the processing plant118 this portion of slurry is chemically processed to remove fissio-nalproducts created during normal reactor operation. The reprocessed slurryof the chemical processing plant 118 can be conveyed to the primaryreactor system by means of a slurry pump 3'18 and valved conduits 120and 121. The conduits 120 and 121 conduct the reprocessed slurry to abattery of high head pumps, indicated generally by the referencecharacters 122, and thence to one of the circulating loops 25 by way ofa valved conduit 124 and one of the branched conduits 104- desoribedheretofore. When not being added to the primary reactor system in thisfashion, the output of the chemical processing plant 118 can be conveyedby means of the slurry pump 318 through a suitable cooler 126, conduits121 and 128, and a valved conduit 130 to the liquid header 110.Alternatively, as in this arrangement when the reactor is not inoperation, the output of the chemical processing plant can be conveyedthrough the cooler 126 and conduit 123 as before, and through anothervalved conduit 13-2 to the slurry accumulator tank 52'A.

However, when filling the primary reactor system including the vessel2%) and associated circulating loops 25, slurry is withdrawn from thedrain tanks 52 in the reversed direction through the valved conduit 13tlor 132 or both, and through the cooler 126 and the associated conduit12?; by means of the aforesaid battery of high head pumps 122 and theconduits 12d and 124. As pointed out previously, the conduit 124 iscoupled to one only of the circulating loops 25 through the associatedone of the branched conduits 104. The liquid header 110 is provided withvalves 134 and 136, which in conjunction with a valve 13% disposed inthe conduit connection 112A of the slurry accumulator tank, determinewhich of the three groups of storage tanks SZ'A, 52'15 or 52C arecoupled to the suction side 141; of the high head pumps 122.

After the reactor system is filled, the primary function of the liquidheader 1112 is to provide for overflow from one storage tank 52' toanother in each group and to assure level equalization among the draintanks in each group. The liquid header 11% also is employed to transferslurry vehicle, which in this case is deuterium oxide, to one or more ofthe drain tanks 52 for purposes of dilution or the like, to transferslurry as subsequently de- 1 storage tanks '52 to the liquid header 11%extend to the bottom of each tank to permit almost complete liquidremoval there-from. These extensions of the conduits 112 are indicatedby dashed lines 142.

After the slurry has been subjected to chain reaction within the reactorvessel 24 and subsequently stored in the drain tanks 52', the slurrywill release a considerable amount of heat due to radioactive decay ofthe contained fission products. The decay heat is removed from thestorage tanks 52 by condensation of that portion of the deuterium oxidevehicle which is vaporized by the decay heat. In furtherance of thispurpose, each of the drain tanks 52 is coupled to the vapor header 144through individual vapor conduit connections 146. That portion of thevapor header 144 which is coupled to the slurry repository tanks '52C isisolated from the remainder of the vapor header 144 by a pair of stopvalves 148. By the same token that portion of the vapor header coupledto the slurry accumulator tank SZA can be isolated from the remainder ofthe vapor header 144, if desired, by means of a normally open valve 150.

More specifically, any heat developed in the slurry accumulator tank52'A and in the six concentrated slurry tanks 52B is removed byconveying the resultant deuterium oxide vapor from these tanks 52'A and52B through the associated valved conduit connections 146, the vaporheader 144, and a valved inlet conduit 152, to a slurry entrainmentseparator 154-. The slurry entrainment separator 154 is a conventional,centrifugal-type device and therefore will not be described in detail.The entrained liquid output of the entrainment separator 154 is returnedto the drain header 96 or to the liquid header through a conduit 156 andvalved conduits 158 and 160, respectively. Thus it is seen that theentrained slurry can be returned to the drain header 96 or to the liquidheader 110 and thence to one or more of the storage tanks 52'A or 52'Bby opening an appropriate one of valves 162 or 164 of the aforesaidconduits 158 or 160.

The vapor from which any entrained slurry has been removed is thenconveyed to an associated drain tank condenser 114 through a conduit166. After being condensed the liquid oxide is conveyed from thecondenser 1 4 through a valved outlet conduit 168 and the valved conduit158 or described heretofore to either the drain header 96 or the liquidheader 110 respectively. A check valve 170 is disposed in the valvedconduit 168 in order to prevent reverse flow of slurry from theentrainment separator 154 which slurry would tend to clog the heatedportions of the condenser 114.

In a similar fashion the vapor removed from the slurry repository tanks52'C and the associated portion of the vapor header 144 is conducted inparallel paths through valved conduits 171 to a pair of slurryentrainment separators 172. The effluent vapors of the slurryentrainment separators 172 are conducted to associated ones of the draintank condensers 115. The outputs of the drain tank condensers 115 and ofthe slurry separators 172 are conveyed respectively through conduits 174and 176 and one of the valved conduits 178 or 189 to either the drainheader 96 or the liquid header 11G, as desired. As stated heretofore thevapor generated in the repository tanks SZC and conducted through thevapor header 144 is normally isolated from the balance of the vaporheader by means of the stop valve 148. Thus, it will be seen that twodrain tank condensers 115 and associated components are reserved for usewith the repository tanks 52C, while one condenser 114 and entrainmentseparator 154- are employed with the balance of the drain tanks. Thisarrangement is necessary due to the larger number of repository tanks52'C and to the fact that these tanks norabsolute by operation of thepressurizing vessel 64. The

pressurizing vessel 64, which desirably contains only deuterium oxide orother such vehicle employed in the homogeneous system as notedheretofore, is separated from the liquid or slurry portion of the surgetank'62 by means of the steam space 68 thereof, to which the conduit 67is coupled, thus avoiding the caking that would result if thecirculating slurry itself-were boiled in the pressurizing vessel-64.

Leaving the reactor vessel the slurry stream branches into four parallelidentical circulating loops only one of which is illustrated in detail.If desired, each loop can be isolated from the reactor by a pair of dualstop valves 328 (FIG. 2) to permit certain types of remote or semidirectmaintenance, without shutting down the entire plant, to be performed onone of the circulating loops, for example, in the manner described inthe aforesaid copending application of McGrath et al., Serial No.659,003, and in a copending application of Webb et 211., Serial No.

659,002, entitled Remote Equipment. Maintenance, filed- May 14, 1957,now abandoned, and also. assigned to the present assignee.

Within the-reactor vessel 20 part of the kinetic energy.

of the fissional fragments is absorbed by the deuterium oxide molecules,some of which are disassociated into deuterium and oxygen gases. For themost part these radiolytic gases are recombined within. the reactorsystem through usage of the palladium catalyst noted above. However, theremaining portion of these radiolytic gases is removed together withcertain gaseous fission products by means of the gas separators andconveyed through the conduit 31 to an external recombining unitassociated with a suitable gas handling system (not shown). Suitableforms of gas handling systems adapted for recombing the radiolytic gasesand for separating and eliminating the fissioned product gases aredisclosed and claimed in copending applications of D. F. Rinald,entitled Radioactive Gas Handling System, Serial No. 691,264, filedOctober 21, 1957, and of]. Weisman et al., entitled Gas Handling Systemfor Radioactive Gases, Serial No. 691,263, filed October 21, 1957, bothof which applica tions are assigned to the assignee of the presentapplication.

From the gas separators 3% the circulating slurry in each loop 25 isconducted to the respective steam generators 32, as noted heretofore.The steam developed in the steam generators is conducted through theoutlet conduits 3'7 and conduits 80 to suitable steam utilizing means,for example, one or more turbo-electric generators (not shown). Inaddition, a small portion of the steam is removed from one of the steamgenerators 32 and returned thereto by means of conduits 82 for thepurpose of supplying heat to various components of the primary reactorsystem. A plurality of storage tanks 84, with two being shown forpurposes of illustration, are coupled to the steam generators by meansof a conduit 36 for purposes of draining the steam side of the steamgenerators in the event of leakage of radioactive slurry into the steamside of the generators or other defect. Any vapor contained at this timewithin the steam generators 32 is removed through overhead conduit 88 toa steam generator drain tank condenser 90. This vapor after beingcondensed in the condenser 90 is conducted to the aforementioned draintanks 84 through a conduit system 92. In the event that the contents ofthe steam generator drain tanks 34 become radioactive the contents canbe conveyed through the valved conduit system 94 to suitable means forconcentrating or otherwise preparing the radioactive material forunderground or oceanic burial.

As indicated heretofore, four circulating loops indicated generally bythe reference. character 25, are associated with the reactor vessel 20;however, in the drawings only one of these loops are shown in detail,inasmuch as in this example these loops are substantially identical.However, as will be described subsequently in greater 10 1 detail, the.piping connections associated with one of the circulating loops 25differs slightly in that certain auxiliary equipment associated with thereactor system are coupled to only one of the circulating loops 25.Inthe case of the. reactor system..described herein, the most importantof these auxiliary systems is the fuel handling system which isillustrated in detail in FIG. 2 of the drawings. In this arrangement,the operationsperforined within the fuel handling system. are dividedinto four major cate-p prises, inter alia, twentydraintanks 52',although only five ofthese tanks are illustrated in FIG. 2. For purposesof exemplifying the invention the drain tanks 52 are grouped into threefunctional categories in which a single drain tank 52'A serves. asaslurry accumulator tank. A total of six drain tanks 52'B serve asstorage for concentrated slurry and the remaining thirteen tanks 52'Cserve as a repository for. the slurry normally circulated through thereactor vessel 20 and the primary coolant loops 25. The latter group oftanks. 52'C are capable of containing the entire contents of the primaryreactor system or about 19,000 gallons and are normally empty duringreactor operation in the event the reactor system must be shut downunder emergency conditions or for purposes of maintenance or othercontingency. The aforementioned drain tank groupings together with thecommon header conduits 96, M0, 144, and 182 are sometimes hereinafterreferred to as the drain tank complex.

Each of these storage tanks 52. is provided with a stirring mechanism59, whichhas been described previously in connection with FIG. 1 of thedrawings. As indicated heretofore none of the generally vertical draintanks 52 contains sutlicient volume to provide a critical mass of thefissile material contained thercwithin. Moreover,' the twenty draintanks 52 are arranged in a separated or spacedarray and desirably areprovided with neutron absorbing material therebetween in order toprevent a critical mass from being formed collectively among the draintanks 52'. A suitable spatial disposition of the drain tanks 52 isdescribed in a copending application of W. A. Webb et al., entitledNuclear Reactor Plant, Serial No. 659,004, filed May. 14, 1957, andassigned to the present assignee.

In this example, the. drain tanks 52' are each approximately three feetin diameter and about thirty feet in height, which dimensions positivelypreclude criticality in the slurry contained within each tank under anycondi tions. Each tank is designed to Withstand an operating pressure of1500 psi. For purposes elaborated upon subsequently, the concentratedslurry contained within the drain tanks 52'B in this example isapproximately double the normal concentration of the slurrycirculatedthrough the primary reactor system.

The drain tank 52A serves as aforesaid, as a slurry accumulator tanknormally used to collect small volumes of slurry periodically dischargedor blown down from various components of the reactor system forcleansing purposes. All the tanks 52' are coupled to a drain header orconduit 96 through individual valved conduits 93. The aforedesoribedgroupings 52'A, 52'B and 52C of the drain tanks 52. are preserved byinsertion of normally closed valves 108 and 102 within the drain header96.

The reactor vessel 20 is ooupledto the drain header 96 by means of aconduit 54 connected to the outlet port 50 of the lower reactor vesselmanifold 22 as described here'- tofore in connection with FIG. 1 of thedrawings. To ensure quick and complete draining of each primary loop 25,the suction side of each primary pump 36 and the inlet of each steamgenerator 32 are connected through a branched conduit system 104 to thedrain header 96. To control draining of the reactor system in thismanner pair of stop valves106 are inserted in each branchof mally areinitially employed to store very'hot slurry, which moreover contains aquantity of fission products as a result of having been subject to thefissional process within the reactor vessel 20. Alternatively, insteadof employing the entrainment separators 154 and 172 for respective onesofthe drain tank condensers 1 14 and 115, a flash section carroe builtinto the vapor space in each drain tank and a suitable entrainmentseparator (not shown) can be included in this space thereby eliminatingthe externaljseparators 154 and 172.

i The storage tanks 52' are provided in addition with a relief header,denoted by the reference character 182. The relief header 182 isconnected to the individual storage tanks 52' by-rneans-of conduits 184containing relief valve 185 and coupled respectively to the vaporconduits 1.46 of each tank 52'. Therelief header 182 is coupled to aninput relief header 186 associated with the deuterium oxide storage tankcondenser 1S8 presently to be described. Likewise, coupled to the inputrelief header 186 by means'of suitable connections (not shown) are othercomponents of the reactor system, as indicated by conduit segments 1%.In order to satisfy the ASME code there are no valves in the reliefheaders 182 and 186 other than the relief valves 185.

Storage space for the slurry vehicle or in this case heavy water isprovided by a plurality of storage tanks 192, with three being employedin this example. During norrnaloperation of the reactor system thesetanks are approximately half full, whereas during a plant shut-down thetanks are completely full. A storage tank condenser 188 is coupled to acommon storage tank outlet conduit 194 through a conduit 196. Any vaporformed in the storage tanks 192 is conducted to the overhead condenser188 by means of an overhead conduit system 198. The outlet conduit 194is coupled to the suctional side of the deuterium oxide pump 2% througha valved conduit 202. When supplying deuterium oxide vehicle to thechemical processing plant 118 for preparation of slurry, makeuppurposes, or the like, the conduit 202 is coupled thereto throughanother valved conduit 264. By means of the pump 2119 the vehicle storedwithin the tanks 192, for purposes noted hereinafter, can be supplied tothe primary reactor system through a conduit 2% which is connected tothe associated branched conduit 104 of one of the circulating loops 25.A check valve 203 is coupled in the conduit 286 in order to preventreverse flow from the primary reactor system or from the high headslurry pumps ,122. With this arrangement the primary reactor system canbe filled initially with deuterium oxide vehicle during the processes ofstarting up and shutting down, presently to be described.

Due to their auxiliary function as catch tanks for relief purposes thedeuterium oxide storage tanks 192 must be limited to a maximum diameterof three feet in this .example inasmuch as it is conceivable that thecirculated -fuel slurry could be conducted to these tanks by way of theinput relief header 186 and storage tank condenser 188. As pointed outpreviously in connection with the drain tanks 52', a tank of thisdiameter is positively incapable of containing a critical mass of theaforesaid fuel slurry. The storage tanks 192 also are employed asaccumulators for liquid or vapor discharged from other components of thereactor plant either normally or during relief situations. Employment ofthese storage tanks 192 as relief volume is desirable inasmuch as theiroperating pressure is relatively low and ranges from about atmosphericto 100 p.s.i.a. The condenser 188 thus serves to limit the maximumpressure during a relief operation and also to remove radioactive decayheat by condensation of the attendant vapors, developed within anyslurry that may be conducted to the deuterium oxide tanks.

The initial quantity of deuterium oxide or other slurry vehicle requiredfor the reactor system is added to the storage tanks 12 from a primarystorage system (not shown) by means of a conduit 210 which joins theoverhead conduit system 198 of the storage tanks 192. Another conduit212 is joined to the outlet side of the deuterium oxide pump 2th),whereby a quantity of the deuterium oxide is supplied to a suitable gashandling system, such as that noted previously, where it serves as adiluent for the radioactive gaseous fission products conveyed throughthe latter-mentioned system. The latter portion of deuterium oxide canbe supplied to an external evaporator (not shown) or one associated withthe gas handling system, and the deuterium oxide steam not used in thegashandling system is returned through a conduit 214 to the storage tankcondenser 188. The D 0 storage tanks and associated components inaddition are pressurized by the aforesaid evaporator to prevent'vaporbinding in the D 0 pump 200.

Slurry concentration and dilution is performed in the drain tank complexor alternatively in the slurry concentrator 22t), presently to bedescribed. The operations of concentration and dilution are undertakenin order to facilitate starting up and shutting down the primary reactorsystem. Concentration in the drain tank complex is done by boiling andutilizes the radioactive decay heat of the slurry itself. The resultantvapor is condensed'in the drain tank condensers 114 and 115 and iscollected inthe deuterium oxide storage tanks 192. In furtherance of thelatter purpose valves 222 and 224 disposed in the outlet conduits 168and 174, respectively, of the drain tank condensers 114 and 115 areclosed; and the condensate, leaving the drain tank condensers 114 or115, is conducted instead to the input relief header 186 and through thedeuterium oxide storage tank condenser 188 through a valved conduit 230and through conduit 226 or 228, respectively. With this arrangement inutilizing the decay heat as aforesaid the desired slurry concentrationcan be obtained ineach group of tanks 52B and SZC.

As indicated heretofore, the concentration of slurry contained withinthe smaller group of drain tanks SZ'B is about double that initiallyconveyed from the primary reactor system to the other group of tanksSZ'C. When the concentration of slurry contained within the repositorytanks 52C is increased in the aforesaid manner to that desired for theconcentrated slurry tanks 52B, for example, the vapor pressure developcdin the tanks 52C can be employed to transfer the contents of the lattertanks to the other group or groups of tanks SZB or SZA depending uponthe storage volume required. In furtherance of this purpose, valves 33iand 336 disposed in the drain and vapor conduits 93c and 1460 of eachrepository tank 52C are closed, whereupon the vapor resulting from decayheat of the slurry within these tanks tends to accumulate atthe topthereof. At the same time a valve 341 in the extended connecting conduit112c-142 of each tank 52/0 and the valve 136 of the liquid header 116are opened whereupon the increasing vapor pressure forces slurry fromthe tanks 52C into the liquid header 110. At this point the other liquidheader valve 134- can be opened and by opening selected ones of valves138 and 341) disposed in the connecting conduits 112a'and 11217 of theaccumulator tank 52A and of the concentrated slurry tanks 52'13, theslurry forced out of tanks 52C can be deposited in one or more of thetanks 52A and 52/13. Alternatively, valves 134 and 342 can be closed,and upon opening valves 320 and 344 in the conduits and 132,respectively, the contents of the repository drain tanks 52"(3, ifrelatively small in quantity, can be conveyed directly to the slurryaccumulator tank SZA in bypassing relationship with the concentratedslurry tanks SZB. The accumulator tank 52'A is then isolated, as innormal operating conditions, from the concentrated slurry tanks SZ'B byclosing the valve 138 situated in the associated connecting conduit112a. Alternatively, slurry can be transferred among the individualdrain tanks 52' of the drain tank complex by coupling selected ones ofthe tanks, from which material is to be removed, to the liquid header110 by opening associated ones of valves 138, 341) and .341 in theconnecting conduits 1120, 112b, and 1120, respectively. The slurry pumps122 are then energized to convey material from the selected tank ortanks via the liquid header 11d and conduit 332 to the drain header 236,after opening valve 333. The material then is deposited in selected onesof the tanks 52 through one or more of the conduits 98a, 28b, and 98cupon opening appropriate ones of their individual valves 335, 337 and334 respectively, and upon opening appropriate ones of the valves 1%,162 and 1 38 in the drain header 96. Still another method oftransferring material among the tanks or removing material from thedrain tank complex involves increasing the pressure of pressurizing Dsteam supplied to the drain header 96 through conduits 317 from anexternal evaporator (not shown) and opening appropriate ones of theaforesaid valves.

Dilution of the slurry in each group of tanks in the drain tank complexis accomplished by bypassing the pump 2% and withdrawing liquiddeuterium oxide from the storage tanks 192 by gravity through conduits202 and 306 to the liquid header 110'. From this point the diluentdeuterium oxide can be diverted to selected groups or individual ones ofthe drain tanks 52' by suitable manipulation of valves 134, 136 and1138. Alternatively, liquid D 0 can be removed from the tanks 192 byincreasing the pressure of D 0 steam supplied thereto through conduit214.

In the event that sufficient decay heat is not available forconcentrating the slurry in this fashion, a slurry concentrator 220 iscoupled to the lower manifold 22 (FIG. 1) of the reactional vessel 20through a valved conduit 238 and a second valved conduit 240. Thusduring normal reactor operation a quantity of slurry can be supplied tothe concentrator 22!) upon opening valves 242 and 244 disposedrespectively in the conduits 238 and 240. When, however, the primaryreactor system is not in operation, the slurry can be drawn from thedrain tanks 52' through the connecting conduits 112, the liquid header110, and associated conduits 130 and 128 by means of the high head pumps122. A valve 246 in the outlet conduit 124 of the pumps 122 is closed inorder to cause the slurry to flow through a valved connecting conduit248 coupled between the outlet conduit 124 and the inlet conduit 240 ofthe slurry concentrator 229. Closing the valve 246, of course, causesthe slurry to flow to the concentrator 220 in bypassing relation to theprimary reactor system.

The slurry concentrator 220 in this arrangement comprises a battery ofhydroclones (not shown), or the like, which are designed for highpressure operation. The hydroclone arrangement, or other centrifugal orseparating device, separates the slurry into dilute and concentratedfractions, which exit from the concentrator 226 through the conduits 250and 252, respectively. Upon opening valve 251 in conduit 250 and closingvalve 253 in the return conduit 3%, the dilute slurry stream isconducted through a suitable cooler 254 to prevent flashing of thedilute and concentrated slurry streams in the depressurizing or letdowndevices, presently to be described. Similarly the concentrated slurrystream is conveyed through cooler 255 by opening valves 255 and 257 inthe conduit .252 and by closing valves 259 and 261 in conduits 296 and298, respectively. The coolers 254 and 256 comprise, for example,ordinary heat exchangers which are designed for the operating pressuresof the reactor system and are coo-led by cooling water supplied theretoby means of conduits 258 and 269.

From the cooler 256 the concentrated slurry stream, which is aboutdouble the normal slurry concentration of the primary system, isconveyed through a slurry letdown device indicated generally by thereference character 262.

The letdown device 262 consists of relatively small diameter tubingdesirably inserted in a suitable cooling medium (not shown) to preventflashing or" the concentrated slurry in the event that the slurry is notsufficiently cooled in the cooler 256, and having sufficient length toinduce the desired pressure drop. At this point the concentrated slurryis added to the drain header 9d and thence to the drain tanks 5 througha valved conduit 264, after the pressure of the slurry has been reducedby the letdown device 262 from the reactor operating pressure of 2000psi. to about 600 p.s.i. or the operating pressure of the drain tanks52'. A check valve 266 is coupled in the drain header 96 between theletdown conduit 264 and the remainder of the components connected to thedrain header in order to prevent reverse fiow from the drain header tothe letdown device and associated components.

A small portion of the slurry concentrated in this fashion isperiodically withdrawn from the outlet stream of the letdown device 262through a valved conduit 267. The latter conduit 267' couples theconcentrated letdown device to a slurry measuring tank 263. With themeasuring tank 263 the amount of concentrated slurry, which periodicallyis extracted from the primary reactor system and is conducted to thechemical processing plant 118 through valved conduit 270, can beproportioned precisely. Any part of the contents of the slurry measuringtank 268 which is not conducted to the chemical processing plant isconveyed to the drain header 96 by means of a valved conduit 272.

The dilute slurry stream issuing from the concentrator 220 is conductedafter passing through the cooler 254 to a depressurizing or letdowndevice indicated generally by the reference character 274. V The letdowndevice 274 is similar in structural detail to the concentrated slurryletdown device 262 and accordingly a further description is dispensedwith. A relatively small portion of the output of the letdown device 274in this arrangement is conveyed to an evaporator 276 through a valvedconduit 278. The remainder of the diluted output is conveyed to the D 0storage tank 192 through a valved conduit 322. In the evaporator 276, aportion of the slurry vehicle, or deuterium oxide in this case, isvaporized by means of process steam (H O) supplied to heating coil 28%.The remaining slurry, after a portion of the vehicle is removed, isconveyed from the bottom or outlet of the evaporator 276 through avalved conduit 282 to the slurry accumulator tank 52A. The vaporgenerated within the evaporator 276 is conveyed to a purge condenser284. In the purge condenser 284, the vaporous vehicle is condensed toform liquid deuterium oxide which is used for purging various componentsof the reactor system in order to prevent accumulation or settling outof slurry particles therein. The purging liquid is supplied to theaforesaid components, as indicated partially by terminal conduits 286,by means of a high head purging pump 288. The purging liquid first isconducted through a cooler 296) in order to prevent vapor binding in thehigh head pump 288. A check valve 292 is disposed in a conduit 294between the cooler 290 and the pump 288 in order to prevent reverse flowin the event of pump failure. The purging system just described in thisexample serves desirably as an auxiliary purging system for use duringreactor shutdown or other contingency. During normal reactor operation,purging liquid is supplied from a fissional gas handling system usuallyassociated with the reactor plant, such as one of the gas-handlingsystems disclosed and claimed and the aforementioned copendingapplications of D. F. Rinald and of I. Weisman et al.

In the event that it is not desired to separate the slurry into lightand heavy fractions by means of the concentrator 220, the concentratorcan be bypassed through the conduits 296 and 252 by opening valves 257and 25) and closing valves 255 and 261. Slurry can then be supplieddirectly from the primary reactor system to the cooler 256 andconcentrated slurry letdown device 262 for depressurizing in the mannerdescribed heretofore and conveyance for instance to the chemicalprocessing plant 118 via the slurry measuring tank 258.

The heavy or dilute fractions issuing from the concentrator 226 can bereturned to the primary reactor system,

for purposes of starting up or shutting down the reactor as explainedmore fully hereinafter, by means of valved conduits 293 and 300, withthe former conduit being coupled to the suctional side of one oftheprimary loop pumps 36. The valved conduits 298 and 3il0-are coupledindividually to the outlet conduits 250 and 252 of the slurryconcentrator 220, and acheck valve 302 or 304 I is connected in each ofthe conduits 293 and 300 in order to prevent reverse flow from theprimary reactor system to the slurry concentrator 220 or to the slurrycoolers 254 and 256. With this arrangement, then, di-

- lute slurry or slurry vehicle can be returned to the-primary reactorsystem inshutting down the reactor by closing valves 251 and 261 and byopening valves 253 and 303 in conduits300 and'293 respectively.Similarly concentrated slurry can be returned, during start-up byopening valves 255, 261 and 303 and by closing valves 253 and 257. Inthis arrangement, the conduit 298 is coupled to the suction side of oneof the circulating pumps 36 to supplythe necessary motive force inreturning the dilute or heavy fractions to the primary reactor system.However, an auxiliary pump can be coupled in the conduit 29%, ifdesired. The rate of return of either the light or heavy fraction isadjusted by suitable setting of the valves 253 or 261, respectively.Motive force for the light or heavy fraction being depress'urized isprovided, or" course, by the pressure drop across the letdown device 274or 262.

The normal process of transferring material into or out of the primaryreactor system is accomplished by means of the D 0 storage tank pump 200and the high head slurry pumps 122, in conjunction with the slurryconcentrator 220. The D 0 storage tank pump 200 is provided in orderinitially to fill the primary reactor system during start-up with heavywater at a relatively high rate and low pressure of about 150 p.s.i.a.,while the high head slurry pumps 122 are employed to transferconcentrated slurry from the drain tanks 52B to the primary reactorsystem at a'considerably lower rate.

the case may be, to the primary reactor system.

As will be described presently in greater detail, the aforementionedlight fraction is fed back into the primary reactor system when its isdesired to dilute gradually the circulated fuel slurry in order toshut-down the reactor in the normal manner. At this time the high headpumps 122 are employed to pump D 0 or very dilute slurry from thestorage tanks 192 to the primary system through conduits 202, 306, 130;128 and 120. On the other hand, the aforesaid heavy fraction is fed backto the primary system in order to increase gradually the concentrationof the circulated slurry when-startingup the reactor. However, during anemergency the entire contents of the primary reactor system may betransferred to the drain tanks 52 rapidly, in this example in aboutfifteen minutes, simply by opening the nine pairs of drain valves 106,three pairs of which are shown in FiG. 2B. This emergency drainageprocedure is avoided if at all possible, because of the high terminalstresses and the erosional damage induced in the drain tank complex andassociated components of the system, when contacted suddenly by thelarge volume of heatedslurry from the primary reactor system. Duringnormal reactor operation this problem is not encountered because onlyrelatively small volumes of slurry are removed from the primary reactorsystem by means of the slurrycorrf 18 'centrator 220. and the dilute andconcentrated slurry letdown devices 274 and 262, respectively.

.In the course of normal reactor operation, approximately 47 gallons ofthe circulated slurry are removed daily, in this example, and conveyedto the chemical processing plant 118 for removal of fissional. productsand other accumulated impurities. This quantity of slurry-is selectedfor processing on the basis that the entire contents of the primaryreactor system, or about 19,000 gallons will be reprocessed over a400-day cycle. As indicated previously, the quantity of slurry thusextracted each day is determined through use of the measuring tank 268.The primary reactor system is replenished with an equal volume of freshslurry from either the concentrated drain tanks SZ'B or from the slurrypreparation facilities (not shown) of the chemical processing plant 118.

When starting up the aforedescribed reactor system, the primary systemis initially filled by means of a socalled push-pull method. In brief,this procedure consists of filling the reactor vessel 20 and the fourassociated primary circulating loops 25 with a slurry vehicle such asliquid deuterium oxide, supplying an over-pressure by means of thepressurizer 64 described heretofore in connection with FIG. 1 of thedrawings so that the primary pumps 36 can be started, and finally addinga slurry of double the final concentration from the drain tanks52;Bwhile at the same time extracting dilute slurry by means of theconcentrator 220 until the desired operating concentration of thereactor is attained. Inthe following Tables I and II the deuterium oxiderequirements and the capacity of the several systems and subsystemsillustrated in FIG. 2 of the drawings are given:

Table I D20 REQUIREMENTS Volume Weight, at F pounds gallons PrimaryReactor System 19, 100 176,700 D20 Sldrry Preparition 7, 150 66,100Minimum far Au-iliary Equipment (approx.)- 1, 500 3,900 Ex ess forAuxiliary Equipment and Reserve Slurry 900 8, 300

Total 28, 650 265, 000

Table II VARIOUS SYSTEM AND SUB-SYSTEM CAPACITIES Gal. Primaryreactor.system 19,100 D 0 storage tanks (192) 21,400 Drain or repository side ofdrain tank complex (52'C) 19,100 Concentrated slurry side of drain tankcomplex "(52'A and SZ'B) 10,300 Auxiiiaryequipment "2, 000

7 header 110 of the drain tank complex. A check valve 308 is disposed inthe connecting conduit 306 to prevent reverse fiow through theconduit306 from the liquid header 110 and the drain tank complex. Theaforementioned 5,650 gallons are withdrawn, of course, asthe D 0 storagetanks 192 are-being filled, inasmuch as the total volume of the storagetanks 192 in this example, is less than the initial D 0 requirements. Anadditional l, 600 gallons are'sent by means of the D 0 storage pump 200and conduit 212 to the evaporator (not shown) employed for example inone of the aforementioned gas handling systems. The latter quantity of DO initially supplies operating purging liquid until the gas handlingsystem attains normal operating conditions.

Prior to adding slurry to the reactor system, it is necessary to obtaina supply of purging water, as aforesaid. As an alternative supply ofpurging water, a portion of the heavy water contained within the storagetanks 192 is transferred by gravity to the evaporator 276 describedheretofore by means of a valved conduit 310. In the evaporator 276 theheavy water is vaporized and subsequently condensed in the purgecondenser 284 as described heretofore in connection with the diluteslurry fraction vehicle. The D withdrawn from the storage tanks 102, isconducted first to the evaporator 276 in order to remove from thepurgewater any slurry par ticles which may have accumulated in the storagetanks. From the condenser 284 the heavy Water is conducted through thecooler 22% and supplied to the suction side of the high head pump 283for purging purposes. From the pump 2% the condensed purge liquid iscarried to a purge storage tank 312 through an outlet conduit 314. Inthe purge storage tank 312 a pressure in excess of the reactor operatingpressure of 2,000 p.s.i.a. is maintained by means of a helium or anotherinert gaseous atmosphere supplied from a suitable pressurized source(not shown). At this point, high pressure water is now available to apurge header 316 which is coupled to those components of the reactorsystem which require purging, for example, the pumps and the entrainmentseparators as indicated by the partial conduits 286.

After a supply of purging water is made available, approximately 7,250gallons of heavy water are transferred to the chemical processing plant113 for preparing the concentrated slurry which is employed as explainedhereinafter for filling the primary reactor system. In order to obtainthe last-mentioned quantity of heavy water, the 5,650 gallons alreadypresent in four of the drain tanks 52C plus the steam condensed duringpressurization of the D 0 storage tanks and the drain tanks aresupplemented by heavy water from the D 0 storage tanks 192. Thepressurizing steam is supplied to the drain tanks 52' from the drainheader 96 via conduit 317, and to the storage tanks 192 through theconduit 214 from a suitable evaporator (not shown). However, at least19,100 gallons must heleft in the storage tanks 192 for initiallyfilling the primary reactor system with the slurry vehicle. The slurryis then returned from the processing plant 118 by means of the transferpump 318 coupled in the outlet conduit 121 of the slurry processingplant. From the pump 313, the concentrated slurry is conducted to theliquid header 110 through the conduits 128 and 130 after opening valves320 and 342. The valve 136 of the liquid header is then closed and thevalve 134 thereof opened with the result that the concentrated slurry isconducted into the concentrated slurry tanks 52B through the individualconduits 112B. At this time the slurry accumulator tank 52'A is isolatedfrom the liquid header 110 by closing its associated valve 138.

The primary reactor system including the reactor 20 and associatedcirculating loops 25 is now filled with the 19,100 gallons of deuteriumoxide or other slurry vehicle contained in the D 0 storage tanks 192, bymeans of the D 0 storage pump 200. Subsequently, the pressurizing vesselis charged with deuterium oxide from a high pressure D 0 storage tank(not shown) via conduit 321. The heaters 70 of the pressurizing vessel64 are then energized to induce an initial pressure of several hundredpounds per square inch within the primary reactor system or a pressuresufficient to prevent vapor binding in the circulating pumps 36. Thefull system pressure of 2,000 p.s.i.a. should not be applied to theprimary system until a temperature of at least 200 F. is attained inorder to avoid the tendency of the structural steels to fracture due tobrittleness at relatively low temperatures. For the same reason, noslurry or circulating fuel is permitted in the primary reactor systemuntil the aforesaid 200 F. temperature level is reached. This precludesthe possibility of a sudden pressure surge or positive system transientbefore the minimum temperature mentioned above is attained.

Accordingly, it is necessary to supply external heat to the primaryreactor system before adding any slurry thereto inasmuch as the initialreactor filling of deuterium oxide is added substantially at roomtemperature. In order to avoid excessive thermal stresses in the heavywalls of the reactor vessel 20, a heating rate of 50 F. per hour isemployed. One arrangement for supplying the necessary heat consists offilling the reactor system with relatively cold deuterium oxide or otherslurry vehicle, operating the primary pumps 36, and thus adding heat aspump work. Alternatively, or in conjunction therewith, heat can be addedto the primary system through the steam generators 32 by means ofprocess (H O) steam supplied to the steam side of one or more of thesteam generators from an external boiler arrangement (not shown).

Before slurry can be introduced into the primary reactor system from theconcentrated slurry drain tanks SZB, the repository drain tanks 52'Cmust be prepared as a safety precaution, for the possibility of anemergency drain. In furtherance of this purpose the tanks of SZC aremaintained at 250 F. or greater at all times. This is accomplished byemptying the drain tanks 52'C and continuously heating them withp.s.i.a. D 0 steam supplied to these tanks through the conduit 317 froman external evaporator, as aforesaid. To heat the tanks SZC from roomtemperature or 60 F. to 250 F. requires the heat equivalent ofapproximately 15,000 pounds of D 0 vapor and the capacity of theexternal evaporator is such that this amount can be generated in fifteenminutes. However, when thermal equilibrium is once obtained, D 0 vaporis condensed at the rate of only pounds per hour in maintaining atemperature of 250 F. in the entire group of the thirteen repositorytanks SZ'C. Additionally, the tanks 52C should be isolated from otherportions of the reactor system so that these other portions will not besubjected to thermal stresses induced by drainage of hot slurry from theprimary reactor system into the repository tanks 52'C. Moreover, thedrain tanks 52'B should likewise be isolated at this time to avoiddiluting the concentrated slurry contained therein.

Slurry is now transferred from the concentrated slurry tanks 52B to theprimary reactor system by means of the high head pumps 122. As theconcentrated slurry is added to the primary reactor system, anequivalent amount of the initial deuterium oxide filling is removed fromthe primary system and this is continued until the desired slurryconcentration is obtained. Removal of the initial deuterium oxidefilling is accomplished by means of the slurry concentrator 220 which isdesigned to withstand an operating pressure in the neighborhood of 2,500p.s.i.a. More specifically, as the concentrated slurry is added to theprimary reactor system from the drain tanks 52'B through conduits 112B,the liquid header 110, the slurry pumps 122, and the conduit 124 asimilar quantity of liquid is extracted from the reactor system byopening valves 242 and 244 in the conduits 238 and 240, respectively,whereupon a quantity of the initial filling is conducted to the slurryconcentrator 220. The heavy or concentrated fraction of the slurryconcentrator output is re turned to the suctional side of one of theprimary pumps: 36 through the conduits 252 and 293 upon openingappropriate valves therein. The light or dilute output of the slurryconcentrator 220 at this time is conducted to the cooler 254 and thedilute slurry letdown device 274 and thence is returned to the D 0storage tanks 102 through the storage tank conduit 1% and a valvedconduit 322. It will be seen from this arrangement that no additionalpump is required for conveying fluid from. the

ing additional fuel to the slurry.

primary system to the slurry concentrator 22h inasmuch as i one of theprimary pumps 36 supplied the driving head.

For a normal shutdown operation the flow paths of the light and heavyfractions issuing from the slurry concentrator 226 are reversed suchthat the heavy fraction is'conveyed to the drain tanks 52 by means ofthe cooler 256, the concentrated slurry letdown device 262, and thedrain header 96. On the other hand, the light fraction of the slurryconcentrator 22 is conveyed through conduits 250, 353i? and 298 to thesuctional side of one of the primary pumps 36; In this manner, theconcentration of the slurry circulating through the primary reactorsystem is diluted gradually until the reactor becomes sub-critical. Of

I course as slurry is conveyed to the slurry concentrator v 120, and thehigh head pumps 122.

During start-up of'the reactor, slurry is fed to the primary reactorsystem at a concentration of approximately 6-3-0 grams of thorium oxideand uranium oxide per kilogram of D 0 and at a rate of 'gallons perminute or less until criticality is reached. During the time in whichconcentrated slurry is added in this fashion the liquid level in thep-ressurizing vessel 64 is maintained constant by controlling the rateof diluted slurry passing through the letdown device 274 The averagetemperature in the centration of about grams per kilogram of D 0 asshown at point 327 on curve 326 in FIG. 3 of the drawings. At this pointof course, the effective coefficient of criticality (k is equal tounity; The slurry must thereafter be introduced at a reduced rate notonly to avoid large inputs of reactivity to the reactor system but alsoto limit the rate of temperature rise to F. per hourand to maintain (k=1). The addition of concentrated slurry is continued until theoperating temperature of 522 F., at substantially zero power level'isreached; This point is designated as the low critical concentration andoccurs in this arrangement at a slurry concentration of about grams perkilogram of D 0 as shown by point 319 on curve 329.

At the low criticality point the reactor desirably is operated at asubstantial percentage of rated power' output in accordance with themethod described and claimed in the aforesaid copending application ofW. A. Frederick as pointed out previously. Alternatively, an externalreactor poison can be added at this time to cause the reactor to becomesubcritical while the concentration of the fuel is being increased tothe high critical concentration. On the other hand, the use of theaforementioned poison can be eliminated altogether and the reactorsystem can be designed to withstand higher peak temperatures andattendant pressures so that the temperature of the circulating slurrycan be permitted to rise sufiiciently to shut down the reactor at thelow critical concentration before add- This is accomplished for exampleby withdrawing only enough steam from the steam generators 32 bysuitably adjusting the valves 324 in their outlet conduits 37 so thattheaverage temperature within the reactor vessel 20 reaches at least 595at which temperature the reactor will remain subcritical, in thearrangement described herein for that oxide to only about 170 grams perkilogram of deuterium oxide. Thus, by removing only a small proportionof power in-the form ot-heatfrom the primarysystem a obtained in thereactor vessel 28 at an average slurry con- 22 resultant temperaturerise prevents the reactor from becoming critical as the concentration isincreased. The resultant expansion of the D 0 vehicle-moderator isillus- 'trated in the following Table III, which expansion results Assoon as the reactor becomes subcritical, heat removal via the steamgenerators 32 is determined substantially to aid in preventing thereactor from again reach ing criticality while the concentration of thefuel is being increased to the operating or high critical concentration.If the reactor is operated for a time at the low critical point, thelimited amount of subsequent fissions plus the decay heat involved byfiissional products generated during the period of criticality willmaintain the temperature of the reactor system at or above theaforementioned temperature of 595 until the concentration can beincreased to the high critical concentration.

After the average reactor temperature of 522 F. has been obtained, whichis the operating temperature in'this case, the temperature is thenmaintained constant by extracting power in the form of heat from theprimary reactor system by means of the steam generators 32. Withdrawingpower, of course, increases the temperature drop across the reactorvessel 20, as illustrated in FIG. 4 of the drawings, while the averagetemperature of the vessel remains constant as shown by'line 345.However, the slurry temperature at the vessel outlet manifold 24(FIG. 1) rises linearly, line 348, with power level until approximately580 F. is attained at fullpower operation; and

' the slurry is supplied to the steam generators 32 at substantially theoutlet manifold temperature. On the other hand, the slurry temperatureat the inlet manifold 22 (FIG. 1) decreases linearly with increasedreactor power output, line 350, to about 465 F. at full reactor power.The temperature of steam issuing from the steam generators 32 decreaseslinearly with the quantity of steam utilized as shown by line 352; thus,the temperature of the steam likewise decreases linearly with increasedreactor power, to about 445 F. at rated power output.

The process of shutting down the reactor system under normal conditions,for example during inspection or maintenance of equipment, requiresessentially the reverse of the steps employed in the aforedescribedstarting up procedure. Initially the heat withdrawn from the reactor isreduced substantially so that the resulting increase of temperature willrender the reactor'subcritical. The reactor then is maintained in asubcritical condition by one of the methods outlined previously whilethe slurry concentration is decreased from the high criticalconcentration to the low concentration.

The slurry concentration is reduced by pumping in 'DO vehicle at therate of 30 gallons per minute and by utilizing the slurry concentrator 22tito return the light or dilute slurry fraction to the primary reactorsystem through conduits 3th) and 293 and to conduct the heavy orconcentrated fraction through the slurry letdown device 262 for storagein the drain tank complex. In furtherance of this purpose, dilute slurryor slurry vehicle, as the casemay be, from the D 0 storage tanks 192 isfed into the primary reactor system by m'eans of the 'high 'headpumps'122 and associated'conduits. The concentration of slurry withinthe primary system should be reduced as'far as" practical in'order'thatfiushing or the spray-ace tain a chain reaction at the low criticalconcentration.

This latter procedure is efficaceous, for example, in maximizing burn-upin a given quantity of slurry, in obtaining fissional products forindustrial purposes, or the like. Following operation at the lowcritical concentration, if used, the chain reaction can be terminatedsimply by reducing the concentration of the slurry, as indicated by theisothermal curves of FIG. 3.

The slurry initially removed from the primary system by the slurryconcentrator 229 is, approximately double the normal concentration andas the concentration in the primary system decreases so will that of theconcentrated output of the slurry concentrator 226. The heavy fractionof the slurry concentrator output is stored in the concentrated slurrytanks SZB to which the heavy fraction. is conveyed by means of conduits252, 26a, and 96 and associated components as described previously.However, after the heavy fraction of the slurry concentrator 229 hasdecreased substantially below double the normal reaction concentrationthe slurry then is reconcentrated by conducting it from the drain tanks52/13 to the concentrator 220 and returning only the heavy fraction tothe drain tanks 'SZB. This is accomplished by conveying the slurrythrough the liquid header 110, conduits 13 and 123, pump bypassingconduit 354, conduit 124, and primary reactor system bypassing conduit 213 to the slurry concentrator inlet conduit 240. Then the heavy fractionis returned via the concentrated slurry letdown device 262. Thenecessary driving force is furnished by heat of radio-active decay, orif the latter is insufficient by an over pressure supplied from theaforesaid external evaporation through conduits 317.

Alternatively, inasmuch as release of radio-active decay heat within theslurry stored in the drain tank 52'B will result in removal of excessslurry vehicle by vaporization, the slurry can be permitted to increaseto the desired consistency without removal from the drain tanks 52B. Thevapors thus removed from the drain tanks are condensed in the drain tankcondensers 114 and 115 as described heretofore and the resultant liquiddesirably is conveyed through the conduits 226, 223 and 239 to the D 0storage tanks 192. After the slurry has been concentrated toapproximately double the normal concentration within the drain tanks52'13 and the concentration of slurry within the primary system has beenreduced to a corresponding concentration of about 30 grams per kilogramof D 0, the pairs of drain valves 1% are opened in the conduits 54 and164, and the slurry is conveyed to the repository tanks 52'C via thedrain header 96 and associated conduits. This low concentration isselected in order to reduce erosion of the drain valves 1% insofar aspractical. More particularly, this concentration is selected because theslurry cannot be criticalized at any temperature at this concentration,as would be indicated by extrapolation of the temperature curves of FIG.3.

During the shutdown procedure decay heat is removed at a lowercontrolled rate from the primary system during the slurry dilutionprocess by reducing the water level at the steam side of the steamgenerators 32. Preheated Obviously, the dilution process can 7 feedwater is employed for this purpose as in the case 7 ,plex desirably ismaintained at this temperature, as described heretofore in connectionwith the start-up pro cedure, so that in the event of emergency drainthe heated slurry conducted to the drain tanks SZC will not sub jectthese tanks to undue thermal stresses.

When the slurry concentration has been reduced to a sumciently low levelthat substantially no slurry particles will settle out in the primarysystem, the primary pumps 36 are shut down, the heaters 70 of thepressurizing vessel 64 are deenergized, and the nine pairs of drainvalves tea are opened, whereupon the contents of the primary system areemptied into the drain tanks SZC, In this manner, thermal shock in thedrain tank complex will be practically nil and erosional damage to thedrain valves 1% will be minimized or eliminated altogether. The pressurein the drain tanks 52' resulting from decay heat is controlled byvarying the cooling Water flow to the drain tank condensers 114 and 115.The maximum pressure of the drain tanks, is arbitrarily set at 600p.s.i.a. although the tanks are designed for 1500 psi. This safetyfactor is desirable inasmuch as available cooling water may beinadequate during an emergency drain.

As indicated heretofore, the slurry concentration in each group of draintanks 52;13 and SZC is controlled by simply changing the fiow path ofthe condensed D 0 vapor from the drain tank condensers 114 and 115. Infurtherance of this purpose, a suitable concentration measuring device(not shown) is associated with each of the drain tanks 52'.

When restarting the reactor the very dilute slurry contained in thedrain tank SZC is forced back into the primary reactor system bysuitable means. The very dilute slurry is withdrawn from the repositorydrain tanks 52'C through the liquid header 119 and associated connectingconduits 112a and thence through conduits 130, i123 and 124 to one ofthe circulating loops 25. In this example, the high head pumps 12.2 areof relatively low volumetric capacity, and therefore, are not employedfor initially filling the reactor vessel 26 and associated circulatingloops 25. For this reason, the high head pumps are bypassed with avalved conduit 354, inasmuch as the initial reactor filling of verydilute slurry is incapable of supporting a chain reaction and can beintroduced at a rapid rate to save time in the restarting procedure.

In one arrangement the driving force required to transfer the diluteslurry from the drain tank complex to the primary reactor system issupplied by means of an overpressure applied in the form of D 0 steamfrom the aforementioned external evaporator. The pressurizing D 0 steamis conveyed to the drain tanks SZC via the conduit 317, the drain header96, and associated connecting conduits 980, after opening appropriatevalves. The increased steam pressure, of course, forces the liquidcontained within the drain tank 52C through the conduits 1120, whichextend as aforesaid to bottoms of the tanks, and into the liquid header119.

In another arrangement the driving force is supplied by heat ofradioactive decay of the slurry contained within the concentrated slurrytanks 5Z'B. Since such material usually is relatively concentrated andcontains, after a period of circulation through the reactor vessel 20, aquantity of fissional products, a considerable amount of D 0 vapor isevolved from the tanks SZ'B by the decay heat of these products. Toemploy this vapor to force the contents of the repository drain tanksSZ'C back into the primary reactor system, valves 356 and 358 are closedin the conduits 152 and 171 connecting the entrainment separators 154and 172 and drain tank condensers 114 and 115, respectively, with thevapor header 144. At the same time, the valves of the vapor header areopened. Valve is also opened it there is an appreciable quantity ofslurry in the slurry accumulator tank 52'A. Any vapor issuing from thetanks 528 and SZA is then conveyed through the vapor header 144 to therepository asserts drain tanks SZC, via their individual connectingconduits 146a after opening valves 336 therein. In this manner the vaporpressure built up in the concentrated slurry tanks S2B is applied to thetop surfaces of the slurry contained within the dilute or repositorydrain tanks SZ'C. As a result the dilute slurry is forced downwardly andout of the drain tank '52C through the connecting conduits 1126 andtheir extensions 142 to the liquid header 110. The valve 134 in theliquid header having been closed, the dilute slurrythen is causedto flowthrough the conduits 130 and 128, the pump bypassing conduit 354, andthe conduit 124 to the primary reactor system. Inasmuch as theconcentration of the slurry contained within the repository tanks SZC isincapable of sustaining a chain reaction, the primary system can becompletely filled with this dilute slurry as an initial step inrestarting the reactor. Thereafter, the concentration of the slurry isincreased in the manner described heretofore in connection withinitially starting the reactor. This arrangement also leaves the tanksSZ'C empty in the event of any contigency or emergency during startingup or subsequent operation of the reactor.

An emergency drain procedure is followed in the event of equipmentleakage or failure in the primary reactor system. A rapid drainage ofthe reactor system obviates such conditions as extensive contaminationof the vapor container (not shown) surrounding the reactor plant,considerable loss of slurry and heavy water or other slurry vehicle, andcaking of slurry in the primary system due to failure of the primarypumps or the like. As shown in FIG. 2 of the drawings the primaryreactor system has a total of nine drain connections with one connection50 being made at the lower or inlet manifold of the reactor vessel 26(FIG. 1) and two connections being made at each of the circulating loops25. As described heretofore, each of these connections is coupledthrough conduits 54 or 194 in each of which are disposed a pair of stopvalves 106. This drainage system permits complete drainage from thelowest points of the entire primary reactor system. In this example, theentire contents of the primary system can be drained in approximatelyfifteen minutes.

If a maximum of radioactive decay heat is produced when the slurry isdrained in this fashion to the drain tanks 52', heat will be generatedtherein for a limited length of time at a greater rate than it can beremoved by the drain tank condensers 114 and 115. During the emergencydrain and for a short period there fte t e temperature and pressure ofthe slurry in the drain tanks will rise to a maximum of about 545 F. and1000 p.s.i.a., in this arrangement.

The drain valves 106 can be operated manually, if desired, oralternatively, these valves can be operated automatically by suitablemechanisms (not shown), which mechanisms are actuated in turn by ahazardous abnormal condition such as an excessively high pressure in theprimary system, detection of radiation in the steam leaving one of thesteam generators 32, loss of power to the primary circulating pumps 36,leakage from the primary reactor system to the aforesaid vaporcontainer, or the like.

From the foregoing description it will be apparent that a novel andetficient reactor system has been described herein. Although theinvention has been described in connection with a particular type ofhomogeneous reactor, it will be apparent that the invention can beadapted readily to other types of homogeneous reactors and relatedreactor systems. The foregoing descriptive and illustrative materialstherefore are intended to exemplify the invention and should not beinterpreted as being limitative thereof. Accordingly, numerousembodiments of the invention will occur to those skilled in the artwithout departing from the spirit and scope of the invention.

Therefore, what is claimed as new is:

l. in a pressurized neutronic reactor system, the combination comprisinga reactor vessel, at least one circulating loop coupled to said vessel,pumping means and heat exchanging means forming part of said loop, saidreactor system being capable of containing a quantity of fluid fuel in avehicle, means coupled to said loop for separating said fluid fuel intodilute and concentrated fractions thereof, valved conduit means forselectively conveying one of said fractions back to said loop, saidvalved conduit means being coupled to the inlet port of said pumpingmeans, pressure let-down means coupled to said separating means and tostorage means for said dilute and said concentrated fractions forreducing the pressure of the remainder of said fractions, valvedconduits for selectively conveying said dilute and said concentratedfractions from said storage means to said loop, fluid-impelling meanscoupled to said last-mentioned conduits, means for substantially fillingsaid loop and said vessel with a quantity of said vehicle containing atmost a diluted quantity of said fluid fuel, whereby upon operation ofsaid separating means said filling can be concentrated by conveying aquantity of said concentrated fraction from at least one of saidseparating means and said storage means to said loop and wherebyconcentrated fuel within said vessel and said loop can be diluted byconveying a quantity of said dilute fraction from at least one of saidseparating means and said storage means to said loop, and conduit meanscoupled between said storage means and the input to said separatingmeans for conveying a selected one of the dilute and the concentratedfractions contained in said storage means to said separating means inbypassing relation with said loop so that said selected fraction can befurther concentrated in said separating means.

2. In a neutronic reactor system, the combination comprising a reactorvessel, means for removing heat from said vessel, said reactor systembeing capable of containing a quantity of fiuid fuel in a vehicle, meanscoupled to said vessel for separating said fluid fuel into dilute andconcentrated fractions thereof, a first valved conduit systern forselectively returning one of said fractions to said vessel, asecondvalved conduit system coupled to said first system for conveyingthe remainder of said fractions to storage means, and conduit meanscoupled between said storage means and the input to said separatingmeans for conveying a selected one of the dilute and the concentratedfractions contained in said storage means to said separating means inbypassing relation with said vessel so that said selected fraction canbe further concentrated in said separating means.

3. In a neutronic reactor system, the combination comprising a reactorvessel, means for removing heat from said vessel, said reactor systembeing capable of containing a quantity of fiuid fuel in a vehicle, meanscoupled to said vessel for separating said fluid fuel into dilute andconcentrated fractions thereof, a first valved conduit system forselectively returning one of said fractions to said vessel, a secondvalved conduit system coupled to said first system for conveying theremainder of said fractions to storage means, conduit means coupledbetween said storage means and the input to said separating means forconveying a selected one of the dilute and the concentrated fractionscontained in said storage means to said separating means in bypassingrelation with said vessel so that said selected fraction can be furtherconcentrated in said separating means, an additional means forselectively adding equivalent dilute and concentrated quantities of saidfluid fuel from an external source to said vessel.

4. In a neutronic reactor system, the combination comprising a reactorvessel, at least one circulating loop coupled to said vessel, pumpingmeans and heat exchanging means forming part of said loop, said reactorsystem being capable of containing a quantity of fluid fuel in avehicle, means coupled to said loop for separating said 27 fluid fuelinto dilute and concentrated fractions thereof, a first valved conduitsystem for selectively returning one of said fractions to said loop, asecond valved conduit systern coupled to said first system for conveyingthe remainder of said fractions to storage means, and conduit meanscoupled between said storage means and the input to said separatingmeans for conveying a selected one of the dilute and the concentratedfractions contained in said storage means to said separating means inbypassing relation with said loop so that said selected fraction can be10 further concentrated in said separating means.

2% References Cited in the file of this patent UNITED STATES PATENTS2,743,225 Ohlinger et a1 Apr. 24, 1956 2,938,844 Graham et a1. May 31,1960 2,990,354 Anderson et a1. June 27, 1961 OTHER REFERENCESWestinghouse Engineer, March 1957, pp. 34-39. Nuclear Power, May 1957,pp. 193-195. Atomics, June 1957, pp. 218, 219, 225.

1. IN A PRESSURIZED NEUTRONIC REACTOR SYSTEM, THE COMLBINATIONCOMPRISING A REACTOR VESSEL, AT LEAST ONE CIRCULATING LOOP COUPLED TOSAID VESSEL, PUMPING MEANS AND HEAT EXCHANGING MEANS FORMING PART OFSAID LOOP, SAID REACTOR SYSTEM BEING CAPABLE OF CONTAINING A QUANITY OFFLUID FUEL IN A VEHICLE, MEANS COUPLED TO SAID LOOP FOR SEPARATINNG SAIDFLUID FUEL INTO DILUTE AND CONNCENTRATED FRACTIONS THEREOF, VALVEDCONDUIT MEANS FOR SELECTIVELY CONVEYING ONE OF SAID FRACTIONS BACK TOSAID LOOP, SAID VALVED CONDUIT MEANS BEING COUPLED TO THE INLET PORT OFSAID PUMPING MEANS, PRESSURE LET-DOWN MEANS COUPLED TO SAID SEPARATINGMEANS AND TO STORAGE MEANS FOR SAID DILUTE AND SAID CONCENTRATEDFRACTIONS FOR REDUCING THE PRESSURE OF THE REMINDER OF SAID FRACTIONS,VALVED CONDUITS FOR SELECTIVELY CONVEYING SAID DILUTE AND SAIDCONCENTRATED FRACTIONS FROM SAID STORAGE MEANS TO SAID LOOP,FLUID-IMPELLING MEANS COUPLED TO SAID LAST MENTIONED CONDUITS, MEANS FORSUBSTANTIALLY FILLING SAID LOOP AND SAID VESSEL WITH A QUANTITY OF SAIDVEHICLE CONTAINING AT MOST A DILUTED QUANTITY OF SAID FLUID FUEL,WHEREBY UPON OPERATION OF SAID SEPARATING MEANS SAID FILLING CAN BECONCENTRATED BY CONVEYING A QUANTITY OF SAID CONCENTRATED FRACTION FROMAT LEAST ONE OF SAID SEPARATING MEANS AND SAID STORAGE MEANS TO SAIDLOOP AND WHEREBY CONCENTRATED FUEL WITHIN SAID VESSEL AND SAID LOOP CANBE DILUTED BY CONVEYING A QUANTITY OF SAID DILUTE FRACTION FROM AT LASTONE OF SAID SEPARATING MEANS AND SAID STORAGE MEANS TO SAID LOOP, ANDCONDUIT MEANS COUPLED BETWEEN SAID STORAGE MEANS AND THE INPUT TO SAIDSEPARATING MEANS FOR CONVEYING A SELECTED ONE OF THE DILUTE AND THECONVENTRATED FRACTIONS CONTAINED IN SAID STORAGE MEANS TO SAIDSEPARATING MEANS IN BYPASSING RELATION WITH SAID LOOP SO THAT SAIDSELECTED FRACTION CAN BE FURTHER CONCENTRATED IN SAID SEPARATIG MEANS.